Excellent motion portrayal is a strong characteristic of cathode ray tubes (CRTs) whereas it is a weakness in many pixelized displays. In particular, motion blur is a limitation of many liquid crystal displays (LCDs). Motion blur in LCDs is caused by various phenomena, one of which is the sample and hold principle of the LCD. Motion blur can be subjectively reduced by modulating the backlight of the display. However, this can introduce flicker. Another option for subjectively reducing motion blur is to increase the frame rate, known as frame rate conversion. This typically relies on a process known as temporal interpolation to create one or more new pictures for placement between two original pictures.
An input video signal whose frame rate is to be increased can consist of several segments of pictures originally taken using video, film and/or other media. For regular video content, which is characterized by the fact that every picture originates at a different moment in time, a 60 Hz input signal can be converted to, say, 120 Hz by placing a single interpolated picture temporally in the middle position between neighboring pictures in the input video signal. However, the situation is different for film material, as film is captured at 24 Hz and (for 60 Hz countries) up-converted by a 3:2 pull down cadence to give a 60 Hz signal. Simply placing a single interpolated picture between each picture of the 3:2 pull down 60 Hz signal to give a resulting output signal at the desired frame rate of 120 Hz would not lead to motion blur reduction at all, and the motion portrayal remains highly irregular in the output signal.
Thus, for film material, motion judder of the film cadence needs to be eliminated prior to up-conversion. This basically means that the 24 Hz original film material is up-converted to 120 Hz by placing 4 new interpolated pictures between neighboring 24 Hz original pictures. Since 80% of the output video now consists of interpolated pictures, the demands of the interpolator are increased. Moreover, perceived picture quality can be severely degraded due to the high proportion of time occupied by interpolated rather than original pictures.
Against this background, there is a need in the industry for a method and system for frame rate conversion based on temporal interpolation, but with improved picture quality and greater computational efficiency than conventional techniques.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.